Medical device and cartridge

ABSTRACT

A cartridge is engageable with a medical device, the cartridge comprising an ordered arrangement of N electrical components ( 540 ) each with different respective values of an electrical property, and an ordered arrangement of N conductors ( 522, 524, 526 ) operably coupled to the ordered arrangement of the N electrical components. A medical device is arranged to receive a cartridge and comprises for each of N conductors on the cartridge, at least a first respective contact arranged to electrically couple with the corresponding conductor when the cartridge is engaged with the medical device; the medical device also comprises an evaluation means operable to evaluate the different respective values of an electrical property of N electrical components on the cartridge, wherein the N electrical components form an ordered arrangement which is operably coupled to the N conductors on the cartridge, and a switching arrangement operable to selectively electrically couple a respective pair of contacts to said evaluation means.

The present invention relates to a medical device and cartridge.

Many medical devices are arranged to use detachable cartridges thatcarry consumable materials. These devices include systems such as pumps,injectors and nebulisers that deliver consumables such as anaesthetics,steroids or other drugs or fluids to a patient.

Clearly, where a range of possible consumable materials is available insimilar cartridges (for example different concentrations of a drug) itis important that a cartridge including the appropriate consumablematerial for the situation is used. Typically this is achieved byselection of the appropriate cartridge by a qualified medicalpractitioner.

However, for patient-operated medical devices such as personal insulininjection systems, such qualified medical supervision is not regularlyavailable and so use of the medical device and the selection of suitableconsumable materials for it depends upon the patient themselves. Thusfor example there is the potential for a patient to administer the wrongtype, or wrong dose, of a drug into their body.

Prior art systems disclose mechanisms for marking such cartridges sothat the medical device can evaluate the cartridge's contentindependently of the user. Such systems include barcodes on thecartridges (U.S. Pat. No. 6,859,673); binary patterns encoded bymetallic or wirelessly inductive strips on the cartridge (U.S. Pat. No.6,110,152, WO0213133, WO1992017231 or WO2007107562), or data representedby the value of one or more resistors (DE4020522, U.S. Pat. No.6,743,202).

However, for very small, lightweight and cheap medical devices such aspersonal insulin injection systems, and similarly for small, lightweightand cheap containers such as insulin cartridges used by such personalinsulin injections systems, the prior art discloses mechanisms that areeither overly complex, require excessive space on the cartridge or aresusceptible to damage or contamination (for example by a spillage ofinsulin, which is electrically conductive).

Therefore there is a requirement for an improved system comprising amachine-identifiable cartridge for use with a medical device.

In a first aspect, a cartridge is engageable with a medical device, thecartridge comprising an ordered arrangement of N electrical componentseach with different respective values of an electrical property, and anordered arrangement of N conductors operably coupled to the orderedarrangement of the N electrical components.

Such an ordered arrangement may take the form of a topologicallytriangular or deltoid arrangement wherein each of the N components has afirst electrical contact and a second electrical contact, the firstelectrical contact of each respective one of the N electrical componentsbeing connected to the second electrical contact of a respective otherof the N electrical components to form N links, and each respective oneof the N links is connected to a respective one of the N conductors.

In a specific form, the conductors and the ordered arrangement of Nelectrical components are mounted on a label that is affixed to an outersurface of the cartridge. The label may extend around the cartridge sothat it overlaps itself. The conductors may be formed so as to extendaround the cartridge circumferentially. In some embodiments, the orderedarrangement of N electrical components is positioned substantially atone end of the ordered arrangement of N conductors. By forming the labelto overlap itself, a continuous or substantial continuos loop ofconductors may be formed so as to cover the ordered arrangement of Nelectrical components. In embodiments where the number of N electricalcomponents are larger than two, this ensures that the loop of conductorsextend with no or only a slight gap in the circumferential direction,without the need for making a multilayer structure to provide thenecessary connections to the N components.

In another aspect, a medical device arranged to receive a cartridgecomprises for each of N conductors on the cartridge at least a firstrespective contact arranged to electrically couple with thecorresponding conductor when the cartridge is engaged with the medicaldevice; the medical device also comprises an evaluation means operableto evaluate the different respective values of an electrical property ofN electrical components on the cartridge, wherein the N electricalcomponents form an ordered arrangement which is operably coupled to theN conductors on the cartridge, and a switching arrangement operable toselectively electrically couple a respective pair of contacts to saidevaluation means.

In a further aspect, a method of manufacturing a cartridge engageablewith a medical device, comprising the steps of selecting a code,responsive to the intended contents of the cartridge, selecting arespective one of M possible values of an electrical property from eachof N non-overlapping sets, associating with the cartridge an orderedarrangement of N electrical components operably coupled to an orderedarrangement of N conductors, wherein each component embodies arespective one of the selected values of the electrical property, andselecting a particular order of the N electrical components with respectto the ordered arrangement of N conductors, wherein the selected ofvalues of electrical properties together with the selected order withrespect to the N conductors of the N electrical components embodyingthese values signify in combination the selected code.

Further respective aspects and features of the invention are defined inthe appended claims.

Embodiments of the present invention will now be described by way ofexample with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a medical device and a cartridge inaccordance with an embodiment of the present invention.

FIGS. 2A and 2B are schematic diagrams of ordered arrangements ofcomponents in accordance with embodiments of the present invention.

FIG. 3 is a schematic diagram of a labelled cartridge in accordance withan embodiment of the present invention.

FIGS. 4A, 4B and 4C are schematic diagrams of electrical contactengagement means in accordance with embodiments of the presentinvention.

FIG. 5 is a schematic diagram of a switching arrangement in accordancewith an embodiment of the present invention.

FIG. 6 is a schematic diagram of an oscillator circuit in accordancewith an embodiment of the present invention.

FIG. 7 is a flow diagram of a method of manufacture of a cartridge inaccordance with an embodiment of the present invention.

A medical device and cartridge are disclosed. In the followingdescription, a number of specific details are presented in order toprovide a thorough understanding of the embodiments of the presentinvention. It will be apparent, however, to a person skilled in the artthat these specific details need not be employed to practise the presentinvention. Conversely, specific details known to the person skilled inthe art are omitted for the purposes of clarity where appropriate.

As a non-limiting example, a summary embodiment of the present inventioncomprises a pen-style personal insulin injector arranged to receive apre-filled medicament cartridge, attached to which are three resistors,a first contact of each sharing a common connection and the secondcontact of each being connected to a respective conductive strip. Theconductive strips are accessible by the injector when the cartridge isproperly engaged with it. Each resistor is chosen to have a resistancevalue selected from a respective one of three non-overlapping sets ofpossible values, so that each resistor has a different value and thatvalue is unique to its respective set. The selection of a value from aset is used to encode information relating to the contents of thecartridge. Likewise, the placement of each resistor within an orderedarrangement (for example, which resistor is connected to whichconductive strip) is also chosen to convey information relating to thecontents of the cartridge, as the use of distinct values fromnon-overlapping sets enables the relative positions of each resistorwith respect to the conducting strips to be evaluated.

In this way a robust encoding of information about the contents of thecartridge can be conveyed in a compact manner. Complementary measures tomitigate against contamination include a non-conductive protective layerover the conductors that is punctured by contacts in the injector whenthe cartridge is engaged, an exposed conductor not connected to thecomponents that indicates contamination if a subsequent electricalconnection is found, and the use of components with complex impedance(resistance) such as capacitors, whose complex impedance is measured atan oscillating frequency where the electrical properties of the presumedcontaminant (here, insulin) are less likely to affect measurement.

Referring now to FIG. 1, in an embodiment of the present invention amedical device in the form of a personal insulin injector 100 comprisesa main body 120 housing a dosing mechanism (not shown), a dose settinginterface 122, and a user interface 124 for displaying information suchas the currently set dosage.

The injector also comprises a detachable cartridge holder 130, intowhich a cartridge 150 may be inserted. The holder is then engaged withthe injector housing, causing the cartridge to be engaged with theinjector dosing mechanism of the injector. The cartridge 150 may be ofthe so-called ‘plunger’ type illustrated in FIG. 1, or may equally be aflexible or collapsible reservoir or any other suitable form.

A needle assembly 140 may then be attached to the cartridge and holderby the screw thread 154 of the cartridge, causing a rear-facing end ofthe needle to puncture a sealed aperture in the cartridge, therebyenabling a flow of insulin into the needle under the control of thedosing mechanism.

In addition, the cartridge comprises an encoding circuit 152 thatembodies a code that can be evaluated by the injector.

Referring now to FIGS. 2A and 2B, the encoding circuit comprises anordered arrangement 540A, 540B of three electrical components (A, B andC), each having a particular and different value of an electricalproperty such as impedance (or complex impedance). Possible componentsinclude resistors, capacitors and/or inductances, or diodes (which havenon-linear impedance).

FIG. 2A shows the three components arranged in a so-called ‘star’configuration, in which one contact of each component shares a commonconnection.

FIG. 2B show the three components arranged in a polygonal (heretriangular) configuration, in which a first contact of each component isconnected to the second contact of one of the other components to form aclosed chain.

In both configurations, three conductor strips (522, 524 and 526) areelectrically coupled to the arrangement of components. In the starconfiguration, each conductor strip connects to the free contact of arespective component. In the triangular configuration, each conductorstrip connects to a respective link between the first and secondcontacts of a pair of components. The conducting strips then typicallyform an ordered sequence of rings around some or all of thecircumference of the cartridge 150.

Advantageously, this arrangement avoids the use of a common or groundconductor, thereby reducing the number of conductors required and henceboth costs and the risk of such a common conductor becoming contaminatedand compromising measurements of all the component values.

Data is encoded using the components in the following manner. Each ofthe three components (A, B and C) has a particular value of anelectrical property that is selected from a respective one of three setsof possible values, and these sets do not overlap. As a non-limitingexample, possible values of impedance may be as given as follows inTable 1:

TABLE 1 Three non-overlapping sets of three possible impedance valuesComponent A B C Value 1 (Ohms) 100 400 1600 Value 2 (Ohms) 200 800 3200Value 3 (Ohms) 300 1200 4800

This gives 3³=27 possible unique combinations of values for thearrangements of A, B and C seen in FIG. 2A or 2B.

Notably, the possible values held by the components A, B or C areuniquely characteristic of those components (or the value sets withwhich the components are associated).

Consequently, therefore, the order in which the components are arrangedwith respect to the conductor strips (522, 524 and 526) can also beuniquely identified. For example, using successive conductor strips on acartridge to test the impedances may result in values 100, 800, 1600being evaluated (using example values from Table 1), meaning thecomponents are arranged as A, B and C with respect to the conductors(for example as seen in FIGS. 2A and 2B). Meanwhile, testing of adifferent cartridge in the same way may result in values 800, 100, 1600,meaning the components are arranged as B, A and C with respect to theconductors.

Therefore the ordering of the components A, B and C with respect to theseries of conducting strips can also be used to convey information. Forthree components, the respective order can be rotated three ways: (A, B,C), (C, A, B), (B, C, A), and these rotations can also be mirrored: (C,B, A), (B, A, C), (A, C, B).

The total number of possible unique combinations with respect to a fixedset of conductors for three components is therefore 27×6 or 162.

More generally, the set of six arrangements of A, B and C above areachieved by swapping successive pairs of components with respect to thethree conductors, as follows:

This approach may then be generalised to more than N=3 components. Forexample, in the case of four components (A, B, C, D) in a star or squareformation analogous to those in FIGS. 2A and 2B, with a correspondingfour sets of non-overlapping values and four conductors, a total of 24unique orderings with respect to the four conductors can be generated bysuccessively swapping pairs of components in the above fashion. Notably,for four non-overlapping sets each of three values, there are 3⁴=81possible unique combinations of values for any one arrangement ofcomponents A, B, C and D. Therefore the total number of possible uniquecombinations is 81×24=1,944.

It will be appreciated that optionally more than M=3 electrical propertyvalues may be available in each set, thereby further increasing thepossible number of unique combinations.

Alternatively, fewer values may be used. Using fewer values simplifiesevaluation, reduces requirements for component value tolerance andmeasurement accuracy, and/or improves robustness to contamination. Forexample, using four components with four non-overlapping sets each onlyhaving two possible electrical property values (e.g. as shown in thenon-limiting example of Table 2 below), then there are 2⁴=16×24=384unique combinations.

TABLE 2 N = 4 non-overlapping sets of M = 2 possible impedance valuesComponent A B C D Value 1 (Ohms) 100 400 1200 3200 Value 2 (Ohms) 200800 1600 4800

In addition, it will be appreciated that unlike a system where eachcomponent may take any value from a single, larger set of possiblevalues (for example where components A, B, C and D could each take anyone of the eight values shown in Table 2, thereby giving 576 possiblecombinations), in embodiments of the present invention if one componentvalue (or values for a pair of components) are affected bycontamination, then identification of the other component valuesprovides information about the contaminated component values by aprocess of elimination (e.g. if values 800, 1200 and 4800 are readaccurately, then the final reading must either correspond to 100 or 200for component A). This assists any attempt to resolve the value of thecontaminated component, thereby making the code more robust tocontamination.

Robustness may be further improved by the use of a redundant codingscheme. For example, in the case of the above arrangement of fourcomponents seen in Table 2, the values of components A and C may becorrelated, as may those of B and D. In this way if any one component iscompromised and returns a value outside the expected range of its set,the information is still available from the corresponding othercomponent. The correlation of non-adjacent components (and by extension,non-adjacent conductors) reduces the risk of a contaminating spillagecompromising both components or conductors of a correlated pair.

It will be appreciated that other coding schemes may also be apparent tothe person skilled in the art.

Referring now to FIG. 3, in an embodiment of the present invention anordered arrangement of components 540 (encompassing a star arrangement540A or a polygonal arrangement such as a triangle or square 540B) ismounted on (e.g. affixed to) a label 510 using known techniques is andis appropriately connected to an ordered arrangement of conductors (522,524, 526) that extend across the width of the label.

Optionally, the width of the label is such that it is greater than thecircumference of the cartridge, so that when the label is wrapped aroundthe cartridge an overlapping portion extends to cover the components andtheir connections to the conductor strips, thereby providing a degree ofprotection to the components from contamination or damage due tohandling. This configuration has the additional benefit that theconducting strips then substantially encircle the cartridge, therebyremoving the requirement for rotational alignment of the cartridge withelectrical contacts in the medical device.

Alternatively, if the label does not overlap then the components may becovered by a non-conductive protective layer, and the conductors thenalso extended over this layer, thereby again substantially encirclingthe cartridge to the extent that the label encircles it. In this caseconnections to the conductors would be provided that extend out fromunder the protective layer to connect the components to the conductivestrip.

Alternatively or in addition, the arrangement of components 540 may allbe clustered, grouped or otherwise positioned at or near one end of theconductor strips, so that only a small proportion of the circumferenceof the cartridge corresponding to the components does not feature theconductors, as seen in FIG. 3.

It will be appreciated that consequently in an embodiment of the presentinvention the label 510 alone, comprising the encoding circuitry andconductors, may be provided separately to conventional cartridges, andonly subsequently applied to such cartridges for example at a packagingplant at a later date.

Alternatively, the components and/or the conductors can be mounted (e.g.affixed) directly on the cartridge in a similar manner, again usingknown techniques. In this case again the components may be clustered ator near one end of the conductor strips, or may be covered by aprotective layer over which the conductors extend.

In the case of mounting the circuitry and conductors on either the labelor directly on the cartridge, in an embodiment of the present inventionthe components may be discrete components or may be part of anintegrated circuit, or may be printed onto the label or cartridge (forexample using resistive inks).

Likewise in the case of mounting the circuitry and conductors on eitherthe label or directly on the cartridge, in an embodiment of the presentinvention a non-conductive protective layer or coating is then appliedover the conductors, and optionally over the components. The coatingserves to shield the conductors (and optionally components) fromelectrically conductive contamination such as a spillage of insulinforming a connection between two conductors and thereby affecting themeasurement of the electrical properties of the components. In use, thecorresponding measurement reading contacts in the medical device push orscrape through this layer to make electrical contact as the cartridge isengaged with the medical device, as explained later herein.

In an embodiment of the present invention, an additional so-called‘verification conductor’ is provided that is not electrically coupled tothe ordered arrangement of components, and is not covered by aprotective layer. In the medical device an additional correspondingcontact is also provided. The medical device can then determine whetherthere is any electrical connection between the additional contact andany of the measurement reading contacts in the medical device, therebyindicating whether a conductive contaminant may be on the surface of thecartridge or have impregnated the label, if present.

The medical device can then alert the user and/or prevent fullengagement of the cartridge (for example by actuation of a blockingmechanism), enabling the user to remove the cartridge and attempt toclean off the contaminant.

Notably, in the case that the other conductors corresponding to theordered arrangement of components are covered by a protective coating,such an electrical connection can be arranged to occur before thecontacts of the medical device puncture the coating (as the contaminantwill lie upon the coating), thereby allowing detection and removal ofthe contaminant before the protection of the coating is compromised.

In the medical device, measurement reading contacts are aligned tocorrespond with the conductors on the cartridge and make an electricalconnection when the cartridge is engaged.

As noted previously, in the case that the conductors connected to theordered arrangement of components are covered by a protective layer, thecorresponding measurement reading contacts push through the protectivelayer to make electrical contact.

Referring now to FIG. 4A, where during engagement of the cartridge themotion of the cartridge holder retaining the cartridge is primarilyaxial with respect to the aperture that receives the cartridge, abridging contact 470′ mounted on the holder (similar, for example, to arelay contact) is arranged to encounter a protrusion 472′ in the body ofthe medical device as the holder is pushed into place, so forcing thebridging contact 470′ through the protective layer (not shown) to theconductor 526 below. The protrusion 472′ comprises the measurementreading electrical contact, thereby making electrical contact with theconductor on the cartridge 150 via the bridging contact 470′. It will beappreciated that only one contact arrangement is shown in FIG. 4A forthe purposes of clarity, and is not limiting.

Referring now to FIG. 4B, where during engagement of the cartridge themotion of the cartridge holder retaining the cartridge is primarilyrotational with respect to the aperture that receives the cartridge, abridging contact 470″ within the cartridge holder (such as, for example,a circle or arc of wire that has protrusions towards and away from thecartridge 150) is arranged to encounter a protrusion 472″ in the body ofthe medical device as the holder is rotated, so forcing a portion of thebridging contact 470″ through the protective layer (not shown) to theconductor 526 below. The protrusion 472″ comprises the measurementreading electrical contact, thereby making electrical contact with theconductor of the cartridge 150 via the bridging contact 470″. It will beappreciated that only one contact arrangement is shown in FIG. 4B forthe purposes of clarity and is not limiting.

Alternatively, in a medical device that does not use a cartridge holderor where it is undesirable to use bridging contacts, other mechanisms todrive the measurement reading contacts thought the protective coating onthe conductor strips of the cartridge will be apparent to the personskilled in the art.

For example referring now to FIG. 4C, a measurement reading contact 474is pivotally mounted within the medical device such that axialengagement of the cartridge with the medical device forces themeasurement reading contact 474 through the protective layer (not shown)to the conductor 526 below. It will be appreciated again that only onecontact arrangement is shown in FIG. 4C for the purposes of clarity andis not limiting.

In a conventional system that used a common ground connection, theelectrical property of each component would be determined by switchablyselecting between the components individually and measuring with respectto the ground connection. However to mitigate against contamination ordamage to such a ground connection, in embodiments of the presentinvention there is no such common ground connection. As a result thevalues of the components must be evaluated by measuring components incombination.

Referring back to FIG. 2A, and using impedance as a non-limitingexample, sequential measurements of impedance between conductors 522 and524, 524 and 526, and finally 526 and 522 result in measurement of theseries impedances of components A+B, B+C and C+A. Since impedances inseries add together it is possible to calculate from these threemeasurements the individual impedances of components A, B and C.

Similarly, referring back to FIG. 2B, and again using impedance as anon-limiting example of electrical property, sequential measurements ofimpedance between conductors 522 and 524, 524 and 526, and finally 526and 522 result in measurement of the impedance of component A inparallel with the series impedance of components B+C (i.e. A∥(B+C)),then B∥(C+A) and finally C∥(A+B). Again in principle these values canthen be used to calculate the individual values of A, B and C.

Referring now to FIG. 5, this second calculation can be simplified by aswitching arrangement that short-circuits one of the impedances in theseries. For example, by closing switches SW₂ and SW₃, component C isshort circuited, and a measurement of A∥B can then be made by closing(i.e. measuring across) switches SW₄ and SW₅ (or alternatively bymeasuring across switches SW₅ and SW₆, which gives the commutative andhence equivalent measurement B∥A). Measurement of B∥C is achieved byclosing switches SW₁ and SW₂ to short circuit component A and measuringacross switches SW₅ and SW₆ or SW₄ and SW₆, whilst C∥A can be measuredby closing switches SW₁ and SW₃ to short circuit component B andmeasuring across switches SW₄ and SW₅ or SW₄ and SW₆. From the measuredvalues of A∥B, B∥C and C∥A, the individual values of A, B and C can becalculated.

This simplified calculation is less sensitive to component tolerancesand measurement accuracy, and hence also to any residual contamination.

In addition, because each combined component value (A∥B, etc) can bemeasured using two possible switch combinations, contamination betweenadjacent conductors can be mitigated by using the alternativelyavailable pair of switches (and hence alternative pair of conductors).Such contamination can be inferred, for example, if the differencebetween a measured value and each of the possible values in thecorresponding value set falls outside a preset tolerance.

It will be appreciated that the above switching arrangement can beextended to four or more components, and so more generally measuresvalues in a triangular, square or other polygonal arrangement ofcomponents by measuring across switches connected across a firstcomponent whilst short-circuiting all other components except apredetermined one in a series that is parallel to that first component.

Referring now to FIG. 6, in an embodiment of the present invention thecomponents used have complex impedances (for example capacitors orinductors, rather than resistors). To measure the impedances (forexample in the form of A∥B, as described above), each component isconnected to an electronic integrator (U1)/comparator (U2) circuit, soforming an oscillator as seen in FIG. 6.

In FIG. 6 the generated frequency is determined primarily by resistor R₄and the combined capacitor presented to the circuit by the switchingarrangement C_(XY) (such as, for example, A∥B). R_(KX) (is thecomparatively small contact resistance, whilst C_(PXY) and R_(PXY) arethe capacitive and resistive characteristics of any contaminants.

Notably, the dielectric properties of insulin (a likely contaminant) arenot constant with frequency. Therefore by careful selection of the valueof resistor R4 and optionally of the values in the N non-overlappingvalue sets used by the N components, a suitable range of resultantfrequencies can be generated that occur where the dielectric propertiesof the insulin (or other cartridge payload if applicable) aresubstantially at their lowest, so further mitigating against the effectsof contamination.

The frequencies so generated are measured at point P in FIG. 6, and maythen be used to determine the presented combined component value (suchas A∥B), and from a plurality of such measurements in sequence theindividuals values of A, B C, etc can be obtained.

It will be appreciated that a similar measurement scheme may be used forthe case where the electrical property of the components is itself aresonant or natural oscillating frequency. For example, the componentsmay comprise crystals (such a quartz or another suitable piezoelectriccrystal), each with a tuned frequency, or alternatively or in additioncomponent pairs such as resistor/capacitor or inductor/capacitor givingrise to a natural oscillating frequency. In this latter case suchfrequency generating circuits may be treated as a single functionalcomponent for the purposes of the coding scheme described herein.

The information provided by the codes may vary in quantity and type. Inthe previous example herein of table 1, where three components and threeassociated non-overlapping sets each comprise three possible electricalproperty values, the total number of possible unique arrangements was162. As a non-limiting example, a 1:1 redundancy in the coding may beapplied (for example using component value correlation, as describedpreviously), resulting in 81 usable codes.

64 of these codes may then be interpreted for example as a set of fivebinary flags, indicating the type of insulin and its concentration.Alternatively each code may be related to a look-up table held in amemory of the medical device, for example by using the code as part of amemory address, to give up to 81 different species of cartridge payload.

Finally, the medical device can act upon the information obtained usingthe code and inform the user of the species of payload within thecartridge. This may take the form of any suitable user interface,including alphanumeric text or an indicator light on the device, orwireless communication to a base unit, etc. Optionally the medicaldevice may also evaluate whether the payload satisfies a usagecondition; for example whether the payload has passed a sell-by date, oris the wrong concentration or type for the time of day or for asequenced drug regime managed by the device. If the evaluation indicatesthat the payload is inapplicable, it may communicate a warning to theuser via a suitable user interface, and/or may prevent administration ofthe payload to the user or require an explicit override from the user todo so.

Referring now to FIG. 7, a method of manufacturing a cartridgeengageable with a medical device comprises:

-   -   in a first step (10), selecting a code, responsive to the        intended contents of the cartridge;    -   in a second step (20), selecting a respective one of M possible        values of an electrical property from each of N non-overlapping        sets;    -   in a third step (30), associating with the cartridge an ordered        arrangement of N electrical components operably coupled to an        ordered arrangement of N conductors, wherein each component        embodies a respective one of the selected values of the        electrical property; and    -   in a fourth step (40), selecting a particular order of the N        electrical components with respect to the ordered arrangement of        N conductors, wherein    -   the selected of values of electrical properties together with        the selected order with respect to the N conductors of the N        electrical components embodying these values signify in        combination the selected code.

It will be apparent to a person skilled in the art that variations inthe above method corresponding to manufacture of the various embodimentsof the apparatus described above are considered within the scope of thepresent invention, including but not limited to:

-   -   i. the components being arranged in a star or polygon topology;    -   ii. the arrangement of components being positioned substantially        at one end of the arrangement of conductors;    -   iii. the electrical property being impedance;    -   iv. the components used being one of resistors, capacitors,        inductors, diodes or any component suitable to embody a specific        value of the chosen electrical property;    -   v. coating the conductors in an insulating, non-porous layer;    -   vi. including a further conductor to detect contamination;    -   vii. associating the components and conductors with the        cartridge by use of glue or other fixing means, or alternatively    -   viii. mounting the components and conductors on a label, and in        this latter case    -   ix. associating the components and conductors with the cartridge        by affixing the label to the cartridge as a further step of        manufacture, optionally so that the label overlaps itself to        protect the (suitably positioned) components.

It will be appreciated that the apparatus disclosed herein may operatein part using conventional hardware suitably adapted as applicable bysoftware instruction or by the inclusion or substitution of dedicatedhardware.

Thus the required adaptation to existing parts of a conventionalequivalent device may be implemented in the form of a computer programproduct comprising processor implementable instructions stored on a datacarrier such as a floppy disk, optical disk, hard disk, PROM, RAM, flashmemory or any combination of these or other storage media, ortransmitted via data signals on a network such as an Ethernet, awireless network, the Internet, or any combination of these of othernetworks, or realised in hardware as an ASIC (application specificintegrated circuit) or an FPGA (field programmable gate array) or otherconfigurable circuit suitable to use in adapting the conventionalequivalent device.

1. A cartridge engageable with a medical device, the cartridgecomprising: an ordered arrangement of N electrical components each withdifferent respective values of an electrical property; and an orderedarrangement of N conductors operably coupled to the ordered arrangementof the N electrical components.
 2. A cartridge according to claim 1,wherein each of the N components has a value of the electrical propertyselected from a respective one of N non-overlapping sets of M possiblevalues of the electrical property.
 3. A cartridge according to claim 2,wherein within the ordered arrangement of N electrical components, theorder of the N electrical components is arranged with respect to theordered arrangement of N conductors to encode information.
 4. Acartridge according to claim 1, wherein each of the N components has afirst electrical contact and a second electrical contact; the firstelectrical contact of each of the N electrical components share a commonconnection; and the second electrical contact of each respective one ofthe N electrical components is connected to a respective one of the Nconductors.
 5. A cartridge according to claim 1, wherein each of the Ncomponents has a first electrical contact and a second electricalcontact; the first electrical contact of each respective one of the Nelectrical components is connected to the second electrical contact of arespective other of the N electrical components to form N links; andeach respective one of the N links is connected to a respective one ofthe N conductors.
 6. A cartridge according to claim 1, wherein theelectrical property is impedance.
 7. A cartridge according to claim 1,wherein all of the N electrical components are one selected from thelist consisting of: i. resistors; ii. capacitors; iii. inductors; andiv. diodes.
 8. A cartridge according to claim 1, comprising a furtherconductor separate to the ordered arrangement of N conductors and notelectrically coupled to the ordered arrangement of N electricalcomponents on the cartridge.
 9. A cartridge according to claim 1,wherein the conductors and the ordered arrangement of N electricalcomponents are mounted on an outer surface of the cartridge.
 10. Acartridge according to claim 1, wherein the conductors and the orderedarrangement of N electrical components are mounted on a label; the labelis affixed to an outer surface of the cartridge; and the label extendsaround the cartridge and overlaps itself to cover the orderedarrangement of N electrical components.
 11. A cartridge according toclaim 1, further comprising a non-conductive protective layer appliedover at least the N conductors.
 12. A label for attachment to acartridge, the cartridge being engageable with a medical device, thelabel comprising: an ordered arrangement of N electrical components eachwith different respective values of an electrical property; and anordered arrangement of N conductors operably coupled to the orderedarrangement of the N electrical components.
 13. A medical devicearranged to receive a cartridge according to claim 1, furthercomprising: for each of N conductors on the cartridge, at least a firstrespective contact arranged to electrically couple with thecorresponding conductor when the cartridge is engaged with the medicaldevice; an evaluation means operable to evaluate the differentrespective values of an electrical property of N electrical componentson the cartridge, wherein the N electrical components form an orderedarrangement which is operably coupled to the N conductors on thecartridge; and a switching arrangement operable to selectivelyelectrically couple a respective pair of contacts to said evaluationmeans.
 14. A medical device according to claim 13, wherein the switchingarrangement is operable to short-circuit all but one component that iselectrically in parallel with a first component currently electricallycoupled to said evaluation means.
 15. A method of manufacturing acartridge engageable with a medical device, the method comprising:selecting a code, responsive to the intended contents of the cartridge;selecting a respective one of M possible values of an electricalproperty from each of N non-overlapping sets; associating with thecartridge an ordered arrangement of N electrical components operablycoupled to an ordered arrangement of N conductors, wherein eachcomponent embodies a respective one of the selected values of theelectrical property; and selecting a particular order of the Nelectrical components with respect to the ordered arrangement of Nconductors, wherein the selected of values of electrical propertiestogether with the selected order with respect to the N conductors of theN electrical components embodying these values signify in combinationthe selected code.